Platelet Extracellular Vesicle Profiles as Biomarkers and Mechanistic Mediators in Nigerian Patients with Sickle Cell Disease: An Original Vesiculomics Investigation

This dissertation characterises platelet-derived extracellular vesicle (pEV) profiles in Nigerian sickle cell disease patients and develops an original vesiculomics framework for understanding their role as both biomarkers and mechanistic mediators of vaso-occlusion and endothelial dysfunction. Extracellular vesicles carry membrane proteins, nucleic acids, and lipid mediators that propagate cellular activation signals in the vascular environment, but their systematic characterisation in SCD has been performed exclusively in non-African populations using different disease-management contexts. Platelet-rich plasma was isolated from 80 HbSS patients in steady state, 40 HbSS patients in vaso-occlusive crisis, and 40 HbAA controls at the National Hospital Abuja. pEVs were isolated by differential ultracentrifugation and characterised by nanoparticle tracking analysis, flow cytometry for surface antigens (CD41a, CD62P, phosphatidylserine), and transmission electron microscopy. Vesicle cargo proteomics was performed by tandem mass spectrometry. pEV functional effects on human umbilical vein endothelial cell (HUVEC) adhesion molecule expression were assessed ex vivo. pEV count and phosphatidylserine exposure were significantly higher in HbSS steady state than controls, and dramatically elevated during crisis. Proteomic analysis identified 24 vesicle cargo proteins differentially abundant in crisis versus steady state, including thrombospondin-1, fibronectin, and complement C3, proposing a novel vaso-occlusive cargo signature. HbSS-derived pEVs induced significantly greater ICAM-1 expression in HUVECs than HbAA pEVs. An original pEV Vaso-Occlusion Mechanistic Model is proposed. Keywords: platelet extracellular vesicles, sickle cell disease, vesiculomics, vaso-occlusion, endothelial dysfunction.